JPS6257004B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a plastic lens held within a lens frame, and particularly relates to a plastic lens that is weakly resistant to temperature and is fixed within the lens frame so that its shape does not change even when the temperature changes. The purpose of this invention is to provide a lens system that maintains lens performance and has strong humidity resistance, and to expand the operating temperature range of plastic lenses and other lenses that do not have temperature resistance.

Conventionally, when a lens, for example, a plastic lens 7, is mounted in a lens frame 2, the back outer peripheral edge 7a of the plastic lens 7 is brought into contact with the lens frame body mounting portion 14 of the lens frame 2, as shown in FIG. 1a. A plastic lens 7 is fitted into the lens frame fitting part 5, and a lens frame screw part 3 screwed onto the inner circumference of the lens frame 2 is fitted with a plastic lens 7.
The presser ring 1 is screwed into the inside of the lens frame 2 while screwing the threaded part 6 screwed on the outer periphery of the presser ring 1, and the contact edge 1a with the plastic lens 7 formed on the inner circumference of the presser ring 1 is connected. , is pressed against the outer peripheral edge 7b of the front side of the plastic lens 7, and the plastic lens 7 is fixed within the lens frame 2.

Now, when the plastic lens 7 having such a configuration is assembled to the lens frame 2 at room temperature and then exposed to a high temperature atmosphere, the linear expansion rate of the molding material of the plastic lens 7 will be different from that of the lens frame 2 and the presser. Because it is larger than the linear expansion rate of the molding material of ring 1,
The clearance of the lens frame fitting portion 5 in the lens frame 2 is reduced.

Furthermore, the first group is most affected by this effect.
Contact part 8 between lens 7 and presser ring 1 in Figure a
(Refer to the enlarged view shown in Fig. 1b), the clearance is already zero when the part is assembled at room temperature, and the forming of the lens 7 and the presser ring 1 occurs in the high temperature atmosphere. The difference in the coefficient of linear expansion of the materials directly affects the surface shape.

That is, the contact portion 8 of the lens 7 and the presser ring 1
In this case, the outer peripheral edge 7b on the front side of the lens 7, which the contact edge 1a of the presser ring 1 presses against, is depressed, and the lens 7 is regulated to a state of zero clearance by the contact edge 1a of the presser ring 1. .

Therefore, as the temperature increases, the plastic lens 7 begins to expand in the radial direction. Thermal stress is generated within the lens 7.

Then, the thermal stress generated inside the plastic lens 7 concentrates on unregulated deformation in the optical axis direction, causing the plastic lens 7 to deform in the optical axis direction.

Considering the cross section in the axial direction including the optical axis of the plastic lens 7, since the length of AB in FIG. becomes smaller.

Now, the length of the arc at room temperature is AB, and it is t℃ below room temperature.
If the length of the arc at high temperature is A'B' and the coefficient of linear expansion of the plastic lens 7 is α, then A'B'≒AB(1+αt) is approximated.

Conversely, when the plastic lens 7 and lens frame 2 assembled together at room temperature are exposed to a low-temperature atmosphere, the linear expansion coefficients of the molding materials of the plastic lens 7, lens frame 2, and presser ring 1 differ as described above. Therefore, as the temperature decreases, the plastic lens 7 contracts more than the lens frame 2 and the presser ring 1, and tends to shrink more than the lens frame 2 and the presser ring 1.
In this case as well, the outer peripheral edge 7b on the front side of the plastic lens 7, which is fixed by pressure contact with the abutting edge 1a of the presser ring 1, is restricted, so that the shrinkage of the plastic lens 7 is prevented as in the case at high temperatures. Presser ring 1
As a result, thermal stress is generated inside the plastic lens 7, and this thermal stress is concentrated in the optical axis direction of the plastic lens 7, which is not restricted by the presser ring 1, causing the plastic lens to shrink. 7 in the optical axis direction.

Therefore, the plastic lens 7 shown in FIG.
Considering the axial cross section including the optical axis of the chord AB
Since the length of is regulated by presser ring 1, the arc
Contraction is concentrated at AB, and as a result, the radius of curvature becomes larger.

Now, if the length of the arc at room temperature is AB, the length of the arc at a temperature lower than room temperature is A'B', and the coefficient of linear expansion of the molding material of the plastic lens 7 is α, then A'B'≒AB・Approximate to (1-αt).

Therefore, from the above, when the plastic lens 7 is attached to the conventional lens frame 2 with the presser ring 1, the radius of curvature of the plastic lens 7 changes due to temperature changes. It is clear that the temperature becomes larger, and that the focus position is significantly shifted and various aberrations are worsened compared to when the temperature is normal.

In addition, in the conventional lens and lens frame configuration, as shown in FIG.
1 and 22, and both lenses 21 and 2.
By interposing the alignment member 24 between the two lenses 2, the two lenses 2 adjacent to each other by their outer peripheral edges can be aligned.
A composite lens constructed to reduce the frictional resistance between lenses 1 and 22 and to prevent lens misalignment between both lenses 21 and 22 was proposed in Japanese Utility Model Application Publication No. 55-138606. ing.

However, in this case, the two lenses 21, 2
The lens 21,
22 is fixed in the fitting part 26 by the holding ring 25, there is no change in the conventional structure, and the lenses 21, 22 have their outer diameters fixed to the fitting part 26 of the lens holding member 23 or the holding ring 25. As with the plastic lens 7, it is impossible to prevent changes in the radius of curvature of both lenses 21 and 22 due to temperature changes, and this prevents shifts in focus position and aggravation of aberrations due to temperature changes. That is impossible.

Therefore, there is a need for a lens holding structure that prevents changes in the radius of curvature that occur due to temperature changes in the conventional lens mounting structure for the lens frame, and that does not cause focus position deviation or worsening of various aberrations, or other lens holding structures. The development of appropriate countermeasures was desperately needed.

Therefore, the present invention proposes a plastic lens that solves the above-mentioned drawbacks of the conventional lens holding device and can meet the above-mentioned demands. Explain.

FIG. 2 is a vertical side view showing an embodiment of the present invention, and the lens frame 31 has a barrel attachment part 40, a lens frame fitting part 34, and a lens frame screw part 36. It is supported by a fitting part 34 and fixed by a presser ring 35 screwed into a lens frame screw part 36.

Now, to explain the plastic lens 50 in the lens holding device having the above-mentioned configuration, a friction reducing portion 33 consisting of a plurality of concentric annular protrusions is formed on the contact surface of the plastic lens body 38 with the lens frame mounting portion 32. Sometimes formed into one piece.

As a result, a small area of contact is formed between the friction reducing portion 33 and the barrel mounting surface. Since the width of the friction reducing portion 33 is narrow, when the lens frame 31 and the plastic lens body 38 thermally expand and the thickness of the plastic lens increases, it absorbs the stress of relative expansion and prevents deformation of the plastic lens body 38 in the thickness direction. prevent. Further, because of this, the contact pressure between the plastic lens 50 and the cladding part 40 does not increase significantly, and the relative expansion of the plastic lens in the radial direction is facilitated. Therefore, within the permissible distance between the plastic lens 50 and the fitting portion 34,
Expands radially without deformation. In the case of normal contact with a small area, the contact friction is large, but in the case of the present invention, the friction reducing portion 33 absorbs the longitudinal expansion during thermal expansion, so the contact pressure does not become large, and furthermore, as with thermal expansion, the contact pressure increases. For slight relative movements, the presence of the friction reducing portion 33 reduces the frictional resistance.

In the illustrated example, the friction reducing portion 33 is formed of a plurality of annular protrusions concentric with the plastic lens body 38, but it does not need to be a complete ring, but may be a part of the ring, and may be formed in the longitudinal direction. Absorption of relative expansion becomes easier. The width, height, number, and length of each protrusion are appropriately selected to avoid deformation of the plastic lens body 38 during longitudinal expansion.

Therefore, in addition to the above configuration, the plastic lens 50 of the present invention includes the plastic lens body 3.
At the outer periphery of the plastic lens body 8, there is a deformation absorbing portion 51 made of a thin piece having a thickness thinner than the minimum thickness of the plastic lens body 38 and extending in a direction substantially perpendicular to the optical axis of the lens; It is constructed by integrally forming a lens frame fitting part 52, which is located at the outer end and is made of an annular member having a wider width than the deformation absorbing part 51.

That is, the thermal stress that tends to occur within the plastic lens body 38 due to temperature changes is concentrated on the deformation absorbing portion 51, and the deformation of this portion is utilized to absorb the stress and prevent the shape change of the plastic lens 50. This is what we are trying to prevent.

Note that the shape of the deformation absorbing portion 51 is not limited to the shape shown in the drawings, and may have a disc shape, a spork shape, a leg shape, etc., and may be formed between the plastic lens body 38 and the lens frame fitting portion 52 This can be implemented by providing a deformation absorbing portion that is thinner than the minimum wall thickness of the deformation absorbing portion.

Further, the lens frame fitting part 52 has an outer periphery fitted to the lens frame fitting part 34, and one end face is located inward from the top of the protrusion, and the other end face is located inside the holding ring 34.
It is configured as a pressing portion pressed by 5.

The effects of the present invention are as follows.

(1) As shown in the above embodiment, a protrusion 33 is provided on the surface of the plastic lens body 38 that attaches to the lens barrel.
By providing a plastic lens 50
The frictional resistance between the plastic lens 50 and the lens frame 31 is attenuated, and the dimensional change of the plastic lens 50 in the radial direction can be realized quite freely. Furthermore, a deformation absorbing portion 51 is provided between the plastic lens 50 and the inner diameter of the lens frame 31.
By interposing the lens, it is possible to hold the lens without play, prevent the plastic lens from changing its shape due to temperature changes, and expand the operating temperature range of the lens system using the plastic lens.

2. Even after assembly, the same performance as when used alone can be maintained, and the design quality of the lens system can be achieved.

[Brief explanation of the drawing]

1a to 1e show the prior art, FIG. 1a is a sectional view showing fixation of the lens and the lens frame,
Figure b is an enlarged view of part A in Figure 1a, Figure 1c is a diagram showing the deformation of the lens due to thermal expansion, Figure 1d is a diagram showing the deformation of the lens due to thermal contraction, and Figure 1e is another known example. FIG. 2 shows an embodiment of the plastic lens of the present invention, and is a longitudinal sectional side view of the plastic lens fixed to a lens frame. 31... Lens frame, 33... Convex strip, 34... Lens frame fitting part, 35... Holding ring, 36... Lens frame screw part, 38... Plastic lens body, 40...
Body attachment part, 50...Plastic lens, 51...
Deformation absorbing part, 52... Lens frame fitting part.

Claims (1)

[Claims] 1. A barrel portion 40 that regulates the position of the lens in the optical axis direction.
and a presser ring 35 for pressing the lens against the barrel portion, the plastic lens body is located on the side end surface of the barrel portion of the plastic body 38 and is substantially concentric with the lens optical axis. Friction reducing portion 33 consisting of an annular or partially annular narrow convex strip
and a deformation absorbing portion 51 that is located on the outer periphery of the plastic lens body and is made of a thin piece that extends in a direction substantially perpendicular to the optical axis of the lens; a pressing part, which is made of an annular member having a wider width than the part, the outer periphery of which fits into the lens frame, one end face of which is located inward from the top of the protrusion, and the other end face of which is pressed by a retaining ring; Mirror frame fitting part 52
A plastic lens characterized by being formed by integrally molding and.